Glass ceramic

ABSTRACT

A glass ceramic having properties of low thermal expansion, high transmittance in a visible light region and low specific gravity, and a glass ceramic substrate made of the glass ceramic are provided. The glass ceramic has a crystal phase containing a β-quartz solid solution precipitated by heat treatment of a matrix glass for a glass ceramic, and the matrix glass has a glass composition comprising 55 to 70 mol % of SiO 2 , 13 to 23 mol % of Al 2 O 3 , 11 to 21 mol % of an alkali metal oxide, provided that the alkali metal oxide contains 10 to 20 mol % of Li 2 O and contains 0.1 to 3 mol % of Na 2 O and K 2 O in total, 0.1 to 4 mol % of TiO 2  and 0.1 to 2 mol % of ZrO 2 , the total content of said components being at least 95 mol %, and further comprising 0 to less than 0.2 mol % of BaO, 0 to less than 0.1 mol % of P 2 O 5 , 0 to less than 0.3 mol % of B 2 O 3  and 0 to leas than 0.1 mol % of SnO 2 .

FIELD OF THE INVENTION

[0001] The present invention relates to a glass ceramic, a glass ceramicsubstrate, an opposite substrate for a liquid crystal panel and adustproof substrate for a liquid crystal panel. More specifically, thepresent invention relates to a glass ceramic having properties such as alow thermal expansion property, a high transmittance in a visible lightregion and a low specific gravity, a glass ceramic substrate that ismade of the above glass ceramic and is suitable for use as a dustproofsubstrate for a liquid crystal projector or a substrate (TFT-oppositesubstrate) facing a substrate with a thin film transistor in a liquidcrystal device, and an opposite substrate and a dustproof substrate fora liquid crystal panel, each of which comprises the above glass ceramic.

PRIOR ART

[0002] A glass ceramic formed by depositing a fine crystal phase in aglass is widely known as a glass having the property of low expansion.For example, JP-B-47-5558 discloses a glass ceramic having a thermalexpansion coefficient of ±0.2×10⁻⁷/° C. at and around room temperature.The glass ceramic is used in the fields of a reflecting mirror of alarge-sized astronomical telescope, a laser gyroscope, a standard or asurface plate and heat-resistant cooking utensils.

[0003] Conventionally, glasses of this type are colored in yellow orbrown even if no colorant is contained, and they have poor transmittanceas compared with general glass, so that their transmittance is often abarrier against the use thereof as a substitute for quartz glass.

[0004] In recent years, a liquid crystal projector is commerciallyavailable as one of large-screen television sets. The key portion of theliquid crystal projector is a liquid crystal panel made of a quartzsubstrate, and dustproof glass substrates for defocusing are attached toboth the surfaces of the liquid crystal panel for preventing theprojection of a foreign matter if such a foreign matter adheres to theliquid crystal panel surfaces. The liquid crystal substrate is formed ofquartz, and essentially, it is desirable to use quartz as the abovedustproof glass. Since, however, quartz glass is expensive,low-expansion transparent glass ceramic is substituted in some liquidcrystal projectors. Similarly, of the two glass substrates constitutinga liquid crystal panel, one on the side where no TFT is formed(“opposite substrate” hereinafter) is replaced with a low-expansiontransparent glass ceramic substrate in some liquid crystal projectors.However, conventional low-expansion transparent glass ceramics have poortransmittance to light in a short wavelength region as compared withquartz glass, so that such ceramics degrade the performance of theliquid crystal projector with regard to screen image qualities.Particularly, conventional low-expansion transparent glass ceramics havelow transmittance at and around 400 nm, and such glass ceramics lookyellow or brown when visually observed. For this reason, projectedimages are inevitably affected by the coloring of the glass ceramics.

[0005] Further, no ultraviolet-curable resin can be used for bonding adustproof glass due to a low transmittance at a wavelength of 400 nm orshorter. It is therefore general practice to use a heat-curable resinfor the bonding. However, the heat-curing procedure takes a time andcauses a productivity problem.

[0006] Further, a molten glass of a low-expansion transparent glassceramic of the above type has a high viscosity, and convection of themolten glass does not easily occur, so that it is difficult to produce ahomogeneous glass. Further, another defect is that the meltingtemperature thereof is high, so that a melting apparatus is greatlylimited or that an ultra-high temperature melting furnace is required,which increases the production cost thereof.

[0007] Further, the transparent glass ceramic of the above type hasanother problem that its crystallization takes a time, so that itsproductivity is low. In the above JP-B-47-7558, Examples describe glassceramics for which the holding time period is 4 to 100 hours at atemperature elevation rate of 8° C./hour. For example, in Example inwhich the holding time period is 24 hours at 800° C., it takes 32 hoursbefore cooling is started.

[0008] Further, most of transparent glass ceramics of the above typehave a specific gravity of 2.5 or more. The specific gravity is animportant factor in use of a transparent glass ceramic including the usein a liquid crystal display. Since quartz glass has a specific gravityof 2.2, such a specific gravity of the glass ceramic sometimes comes tobe a barrier against a use thereof as a substitute for the quartz glass.

[0009] Under the circumstances, attempts have been made in various waysto improve low-expansion transparent glass ceramics in transmittance andmelting properties.

[0010] For example, JP-A-3-23237 and JP-A-2-293345 describe glassceramics containing no TiO₂. It is said that Ti ion in the co-presenceof impurities such as Fe ion, etc., greatly colors a glass ceramic, andit has been attempted to prevent the coloring by incorporating such Tiion. In the above glass ceramic, TiO₂ is a nucleating component of theglass ceramic and is therefore replaced with ZrO₂. Since, however, ZrO₂is a component that is not easily dissolved in glass, it is liable toremain, and it is difficult to produce a homogeneous glass, so that itsmelting requires a high temperature of approximately 1,600° C.

[0011] Japanese Patent 2,516,537 discloses a low-expansion transparentglass ceramic containing 3 to 6% by weight of Li₂O and substantiallycontaining none of Na₂O and K₂O. However, since the above glass containsnone of Na₂O and K₂O, and further since the content of Li₂O is 6% byweight or less, it has a high melt viscosity, so that homogenizationtakes a time. Further, since the above glass ceramic contains none ofNa₂O and K₂O that are components for suppressing the crystallizationrate, the crystallization rate of the glass increases, and the glassduring the crystallization is liable to undergo cracking. It istherefore required to decrease the temperature elevation rate, or holdthe glass at a relatively low temperature for a long period of time, sothat the crystallization does not sharply take place and that thecracking is accordingly prevented. For example, Example of the aboveJapanese Patent describes holding time periods of 10 hours at anucleating temperature and 10 hours at a crystal growth temperature. Inany case, the crystallization takes a long time and is liable todecrease the productivity of the glass ceramic. The glass ceramic isimproved in transparency as compared with conventional products, whilethe transmittance thereof is low at and around 400 nm, and its color isyellowish. The glass ceramic of the above Japanese Patent is thereforehardly suitable for use in a display.

DISCLOSURE OF THE INVENTION

[0012] Under the circumstances, it is an object of the present inventionto provide a glass ceramic which is easily meltable and has propertiessuch as a low thermal expansion property, a high transmittance in avisible light region and a low specific gravity imparted by carrying outcrystallization treatment for a short period of time, a glass ceramicsubstrate formed of the above glass ceramic, and an opposite substrateand a dustproof substrate for a liquid crystal panel, each of whichcomprises the above glass ceramic.

[0013] For achieving the above object, the present inventors have madediligent studies and as a result has found that a glass ceramic having acrystal phase containing β-quartz solid solution precipitated by heattreatment of a glass ceramic matrix glass having a specific compositionor a glass ceramic having a crystal phase containing a β-quartz solidsolution and having specific physical properties suits the aboveobjects. The present invention has been completed on the basis of theabove findings.

[0014] That is, the present invention provides:

[0015] (1) A glass ceramic having a crystal phase containing a β-quartzsolid solution precipitated by heat treatment of a matrix glass for aglass ceramic, the matrix glass having a glass composition comprising 55to 70 mol % of SiO₂, 13 to 23 mol % of Al₂O₃, 11 to 21 mol % of analkali metal oxide, provided that the alkali metal oxide contains 10 to20 mol % of Li₂O and contains 0.1 to 3 mol % of Na₂O and K₂O in total,0.1 to 4 mol % of TiO₂ and 0.1 to 2 mol % of ZrO₂, the total content ofsaid components being at least 95 mol %, and further comprising 0 toless than 0.2 mol % of BaO, 0 to less than 0.1 mol % of P₂O₅, 0 to lessthan 0.3 mol % of B₂O₃ and 0 to leas than 0.1 mol % of SnO₂ (to bereferred to as “glass ceramic I” hereinafter).

[0016] (2) A glass ceramic as recited in the above (1), wherein theglass matrix contains at least one component selected from the groupconsisting of Cs₂O, MgO, CaO, SrO, ZnO, La₂O₃, Nb₂O₅, Y₂O₃, Bi₂O₃, WO₃,As₂O₃, Sb₂O₃, F and SO₃, and the total content of the at least onecomponent selected from said group and BaO, P₂O₅, B₂O₃ and SnO₂ is 5 mol% or less.

[0017] (3) A glass ceramic having a crystal phase containing a β-quartzsolid solution precipitated by heat treatment of a matrix glass for aglass ceramic and having a spectral transmittance of at least 70% at 400to 750 nm when it has a thickness of 5 mm, the matrix glass having aglass composition comprising 55 to 70 mol % of SiO₂, 13 to 23 mol % ofAl₂O₃, 11 to 21 mol % of alkali metal oxides, provided that the contentof Li₂O is 10 to 20 mol % and that the total content of Na₂O and K₂O is0.1 to 3 mol %, 0.1 to 4 mol % of TiO₂ and 0.1 to 2 mol % of ZrO₂, thetotal content of said components being at least 95 mol % (to be referredto as “glass ceramic II-1” hereinafter).

[0018] (4) A glass ceramic having a crystal phase containing a β-quartzsolid solution precipitated by heat treatment of a matrix glass for aglass ceramic and having a spectral transmittance of at least 85% at 400to 750 nm when it has a thickness of 1.1 mm, the matrix glass having aglass composition comprising 55 to 70 mol % of SiO₂, 13 to 23 mol % ofAl₂O₃, 11 to 21 mol % of an alkali metal oxide, provided that the alkalimetal oxide contains 10 to 20 mol % of Li₂O and contains 0.1 to 3 mol %of Na₂O and K₂O in total, 0.1 to 4 mol % of TiO₂ and 0.1 to 2 mol % ofZrO₂, the total content of said components being at least 95 mol % (tobe referred to as “glass ceramic II-2” hereinafter).

[0019] (5) A glass ceramic as recited in the above (3) or (4), whereinthe matrix glass contains 5 mol % or less of at least one componentselected from the group consisting of Cs₂O, MgO, CaO, SrO, BaO, ZnO,La₂O₃, Nb₂O₅, Y₂O₃, Bi₂O₃, WO₃, P₂O₅, B₂O₃, As₂O₃, Sb₂O₃, SnO₂, F andSO₃.

[0020] (6) A glass ceramic as recited in one of the above (1) to (5),which has an average linear expansion coefficient of from −10×10⁻⁷/° C.to +10×10⁻⁷/° C. in a temperature range of from 30° C. to 300° C.

[0021] (7) A glass ceramic having a crystal phase containing a β-quartzsolid solution, having a spectral transmittance of at least 70% at 400to 750 nm when it has a thickness of 5 mm, and having an average linearexpansion coefficient of from −10×10⁻⁷/° C. to +10×10⁻⁷/° C. in atemperature range of from 30° C. to 300° C. (to be referred to as “glassceramic III-1” hereinafter).

[0022] (8) A glass ceramic having a crystal phase containing a β-quartzsolid solution, having a spectral transmittance of at least 85% at 400to 750 nm when it has a thickness of 1.1 mm, and having an averagelinear expansion coefficient of from −10×10⁻⁷/° C. to +10×10⁻⁷/° C. in atemperature range of from 30° C. to 300° C. (to be referred to as “glassceramic III-2” hereinafter).

[0023] (9) A glass ceramic as recited in one of the above (1) to (8),wherein the crystal phase has a volume of at least 50% based on thetotal volume of the glass ceramic.

[0024] (10) A glass ceramic as recited in one of the above (1) to (9),wherein the crystal phase has an average crystal grain size of 5 to 100nm.

[0025] (11) A glass ceramic as recited in one of the above (1) to (10),which has a specific gravity of 2.2 or more but less than 2.5.

[0026] (12) A glass ceramic substrate made of the glass ceramic asrecited in one of the above (1) to (11).

[0027] (13) An opposite substrate for use in a liquid crystal panelhaving a light-transmitting substrate and an opposite electrode formedthereon, the light-transmitting substrate being the glass ceramicsubstrate as recited in the above (12).

[0028] (14) An opposite substrate as recited in the above (13), whereinthe liquid crystal panel has (a) a driving substrate having a substrate,a pixel electrode formed on said substrate and a switching elementconnected to said pixel electrode, (b) an opposite substrate that ispositioned opposite to said driving substrate through a predeterminedspace and has a light-transmitting substrate and an opposite electrodein a position being on said light-transmitting substrate and facing saidpixel electrode, and (c) a liquid crystal layer which is held in apredetermined space formed between said driving substrate and a drivingsubstrate and is drivable by a voltage upon application of the voltagebetween said pixel electrode and the opposite electrode.

[0029] (15) An opposite substrate as recited in the above (14), whichfurther has a light-shielding film formed in a position that is oppositeto the switching element of the driving substrate and is on thelight-transmitting substrate.

[0030] (16) A dustproof substrate for a liquid crystal panel having atransparent substrate and an anti-reflection film formed thereon, thetransparent substrate being the glass ceramic substrate recited in theabove (12).

[0031] (17) A dustproof substrate for a liquid crystal panel having atransparent substrate and an anti-reflection film formed thereon, thetransparent substrate being made of a glass ceramic substrate which hasa spectral transmittance of at least 70% at 400 to 750 nm when it has athickness of 5 mm.

[0032] (18) A dustproof substrate for a liquid crystal panel having atransparent substrate and an anti-reflection film formed thereon, thetransparent substrate being made of a glass ceramic substrate which hasa spectral transmittance of at least 85% at 400 to 750 nm when it has athickness of 1.1 mm.

[0033] (19) A dustproof substrate as recited in the above (17) or (18),wherein the glass ceramic substrate has a crystal phase containing aβ-quartz solid solution and has an average linear expansion coefficientof from −5×10⁻⁷/° C. to +5×10⁻⁷/° C. in a temperature range of from 30°C. to 300° C.

[0034] (20) A dustproof substrate as recited in the above (17), (18) or(19), wherein the glass ceramic substrate has a specific gravity of atleast 2.2 but less than 2.5.

[0035] (21) A dust proof substrate as recited in one of the above (16)to (20), wherein the liquid crystal panel has (a) a driving substratehaving a substrate, a pixel electrode formed on said substrate and aswitching element connected to said pixel electrode, (b) an oppositesubstrate that is positioned opposite to said driving substrate througha predetermined space and has a light-transmitting substrate and anopposite electrode in a position being on said light-transmittingsubstrate and facing said pixel electrode, and (c) a liquid crystallayer which is held in a predetermined space formed between said drivingsubstrate and an opposite substrate and is drivable by a voltage uponapplication of the voltage between said pixel electrode and the oppositeelectrode,

[0036]  the dustproof substrate being for use on an outer surface of atleast one of said driving substrate and said opposite substrate.

BRIEF DESCRIPTION OF DRAWINGS

[0037]FIG. 1 schematically shows one example of structure of a liquidcrystal panel having a dustproof substrate.

[0038]FIG. 2 schematically shows an opposite substrate in Example 11 ofthe present invention.

[0039]FIG. 3 schematically shows the steps of producing an oppositesubstrate in Example 12 of the present invention.

[0040]FIG. 4 schematically shows a dustproof substrate of Example 13 ofthe present invention.

EMBODIMENTS OF THE INVENTION

[0041] The glass ceramic of the present invention includes the followingthree embodiments, a glass ceramic I, a glass ceramic II and a glassceramic III. Further, the glass ceramic II includes glass ceramics II-1and II-2, and the glass ceramic III includes glass ceramics III-1 andIII-2.

[0042] That is, the glass ceramic I has a crystal phase containing aβ-quartz solid solution precipitated by heat treatment of a matrix glassfor a ceramic glass, the matrix glass having a glass compositioncomprising 55 to 70 mol % of SiO₂, 13 to 23 mol % of Al₂O₃, 11 to 21 mol% of an alkali metal oxide, provided that the alkali metal oxidecontains 10 to 20 mol % of Li₂O and contains 0.1 to 3 mol % of Na₂O andK₂O in total, 0.1 to 4 mol % of TiO₂ and 0.1 to 2 mol % of ZrO₂, thetotal content of said components being at least 95 mol %, and furthercomprising 0 to less than 0.2 mol % of BaO, 0 to less than 0.1 mol % ofP₂O₅, 0 to less than 0.3 mol % of B₂O₃ and 0 to leas than 0.1 mol % ofSnO₂.

[0043] The glass ceramic II includes a glass ceramic II-1 and a glassceramic II-2. The glass ceramic II-1 has a crystal phase containingβ-quartz solid solution precipitated by heat treatment of a matrix glassfor a glass ceramic and has a spectral transmittance of at least 70% at400 to 750 nm when it has a thickness of 5 mm, the matrix glass having aglass composition comprising 55 to 70 mol % of SiO₂, 13 to 23 mol % ofAl₂O₃, 11 to 21 mol % of alkali metal oxides, provided that the contentof Li₂O is 10 to 20 mol % and that the total content of Na₂O and K₂O is0.1 to 3 mol %, 0.1 to 4 mol % of TiO₂ and 0.1 to 2 mol % of ZrO₂, thetotal content of said components being at least 95 mol %.

[0044] The glass ceramic II-2 has a crystal phase containing a β-quartzsolid solution precipitated by heat treatment of a matrix glass for aglass ceramic and has a spectral transmittance of at least 85% at 400 to750 nm when it has a thickness of 1.1 mm, the matrix glass having aglass composition comprising 55 to 70 mol % of SiO₂, 13 to 23 mol % ofAl₂O₃, 11 to 21 mol % of alkali metal oxides, provided that the contentof Li₂O is 10 to 20 mol % and that the total content of Na₂O and K₂O is0.1 to 3 mol %, 0.1 to 4 mol % of TiO₂ and 0.1 to 2 mol % of ZrO₂, thetotal content of said components being at least 95 mol %.

[0045] The glass ceramic III includes a glass ceramic III-1 and a glassceramic III-2. The glass ceramic III-1 has a crystal phase containing aβ-quartz solid solution, having a spectral transmittance of at least 70%at 400 to 750 nm when it has a thickness of 5 mm, and has an averagelinear expansion coefficient of from −10×10⁻⁷/° C. to +10×10⁻⁷/° C. in atemperature range of from 30° C. to 300° C. The glass ceramic III-2 hasa crystal phase containing a β-quartz solid solution, having a spectraltransmittance of at least 85% at 400 to 750 nm when it has a thicknessof 1.1 mm, and has an average linear expansion coefficient of from−10×10⁻⁷/° C. to +10×10⁻⁷/° C. in a temperature range of from 30° C. to300° C.

[0046] First, the glass ceramics I and II will be explained below.

[0047] The matrix glass for the glass ceramics I and II has acharacteristic feature in that the content of alkali metal componentssuch as Li₂O, Na₂O, K₂O and the like is greater than that in anyconventional low-expansion transparent glass ceramic. The above featureproduces the following advantages. {circle over (1)} The melt viscosityof the glass is decreased, so that a homogeneous glass ceramic can beeasily produced. {circle over (2)} The melting temperature of the glasscan be decreased, so that the limitation to a melting apparatus can bedecreased. {circle over (3)} The melting temperature of the glass islow, and impurities from a container or a refractory material aretherefore not easily included in the glass during the melting of theglass, so that the coloring of the glass ceramic can be controlled to bea low level. {circle over (4)} The glass during its crystallization isfree from cracking even if the crystallization time period is decreased,so that the production cost thereof can be decreased. {circle over (5)}The specific gravity of the glass ceramic can be decreased.

[0048] It is said that when a conventional glass has an Li₂O content inthe range specified in the present invention, a crystal precipitated hasa large size and greatly impairs the transparency of the glass ceramic(Japanese Patent No. 2,516,537). The present inventors have found thateven when the content of Li₂O is increased, the formation of alarge-sized crystal can be prevented by controlling the crystalprecipitation on the basis of other component.

[0049] Further, the following has been found. Since the matrix glasscontains at least 11 mol % of an alkali metal oxide, the melt viscosityof the glass is decreased, and the convection of the molten glass ispromoted, so that the glass is improved in uniformity. Further, themelting temperature of the glass is decreased, and the coloring causedby inclusion of foreign matte from a container with the molten glass init can be prevented. At the same time, the specific gravity of the glasscan be decreased.

[0050] It is also another feature that the matrix glass for a glassceramic, provided by the present invention, contains a relatively largeamount of Na₂O and/or K₂O. In conventional transparent glass ceramic,the content of the above alkali metal component that increases a thermalexpansion coefficient is controlled to be as low as possible(JP-A-62-182135).

[0051] The present inventors have found that a glass ceramic having anaverage linear expansion coefficient of from −10×10⁻⁷/° C. to +10×10⁻⁷/°C. in a temperature range of from 30 to 300° C. can be obtained from amatrix glass having a glass composition that can attain a well balanceon the basis of an increase in a precipitated crystal amount even if thecontent of Na₂O and/or K₂O is increased.

[0052] The matrix glass is heat-treated for crystallization, wherebythere can be obtained a glass ceramic in which a crystal phase isdispersed in an amorphous phase. Of the precipitated crystal phases, theamount of a β-quartz solid solution and/or a β-eucryptite solid solution(these will be referred to as “β-quartz solid solution” hereinafter) isthe largest. Of these, preferably, a crystal phase of the β-quartz solidsolution alone is precipitated. Further, preferably, the crystal phasehas a size of approximately 5 to 100 nm, and the volume of the crystalphase in the glass ceramic is approximately at least 50%.

[0053] Further, Na₂O and/or K₂O have or has not only the effect ofpreventing the crystallization of the glass thereby to prevent thefogging or coloring of the glass ceramic but also the effect ofsuppressing cracking during crystallization. The temperature elevationrate in the crystallization treatment can be therefore increased, sothat the time period for the treatment can be decreased.

[0054] The amount ranges of components of the glass composition of thematrix glass for the glass ceramics I and II of the present inventionwill be explained below.

[0055] SiO₂ is a basic glass component and essential for forming aβ-quartz solid solution. When the content of SiO₂ is less than 55 mol %,the devitrification resistance is degraded, and no transparent glassceramic can be obtained. When it exceeds 70 mo %, it is difficult tomelt the glass. The content of SiO₂ is therefore limited to 55 to 70 mol%. It is preferably 63 to 68 mol %.

[0056] Al₂O₃ is also an essential component for precipitating a β-quartzsolid solution. When the content of Al₂O₃ is less than 13 mol %, acoarse crystal is formed, and no transparent glass can be obtained. Whenit exceeds 23 mol %, the devitrification resistance of the glass isdegraded, and the glass ceramic is liable to be cloudy. The content ofAl₂O₃ is therefore limited to 13 to 23 mol %, and it is preferably 15 to20 mol %.

[0057] Li₂O is also an essential component for precipitating a β-quartzsolid solution. When the content of Li₂O is less than 10 mol %, theglass has a high viscosity, so that the glass is hard to melt. When itexceeds 20 mol %, a coarse crystal is formed, and no transparent glassceramic can be obtained. The content of Li₂O is therefore limited to 10to 20 mol %, and it is preferably 12 to 17 mol %.

[0058] Na₂O and K₂O are important components for improving the glass inmeltability and also for adjusting thermal expansion properties,controlling the crystallization rate of the glass and preventing theclouding and cracking of the glass. When the total content of Na₂O andK₂O is less than 0.1 mol %, the above effects cannot be accomplished.When the above total content exceeds 3 mol %, the glass is liable tohave a large thermal expansion coefficient. The total content of Na₂Oand K₂O is therefore limited to 0.1 to 3 mol %, and it is preferably 0.5to 2 mol %, more preferably 1 to 2 mol %.

[0059] When the total content of the alkali metal oxides is less than 11mol %, the glass has a high viscosity, and it is difficult to produce ahomogeneous glass. When it exceeds 21 mol %, it is difficult to preventthe formation of a coarse crystal, and no colorless and transparentglass ceramic can be obtained. The total content of the alkali metaloxides is therefore limited to 11 to 21 mol %, and it is preferably 12to 17 mol %.

[0060] TiO₂ is an important component for forming a crystal nucleus.When the content of TiO₂ is less than 0.1 mol %, there is produced noeffect thereof, and crystallization does not easily take place duringheat treatment. When it exceeds 4 mol %, the devitrification resistanceis degraded. The content of TiO₂ is therefore limited to 0.1 to 4 mol %,and it is preferably 1 to 3 mol %.

[0061] As described already, the co-presence of Ti ion and Fe iongreatly colors the glass ceramic. However, the present invention usesraw materials of an optical glass grade, so that the glass ceramic ofthe present invention substantially contains no Fe ion. Therefore, acolorless transparent glass ceramic can be obtained although it containsTiO₂. The content of ZrO₂ can be made smaller than the content of ZrO₂that is conventionally used alone as a nucleating component. As aresult, the melting temperature can be decreased, and finer crystals canbe precipitated due to the co-presence of TiO₂ and ZrO₂, which furtherresults in an improvement in the transmittance of the ceramic glass.

[0062] ZrO₂ is also an important component for precipitating a finecrystal when used as a component for forming a crystal nucleus, incombination with TiO₂. When the content of ZrO₂ is less than 0.1 mol %,the effect thereof is not produced. When it exceeds 2 mol %, the glassis hard to melt. The content of ZrO₂ is therefore limited to 0.1 to 2mol %, and it is preferably 0.5 to 1.5 mol %.

[0063] Although not being any essential components, Cs₂O, MgO, CaO, SrO,BaO, ZnO, La₂O₃, Nb₂O₅, Y₂O₃, Bi₂O₃, WO₃, P₂O₅, B₂O₃, As₂O₃, Sb₂O₃,SnO₂, F and SO₃ can be used as required in a total amount of 5 mol % orless for decreasing the melt viscosity, clarification and adjusting thethermal expansion coefficient and the transmittance. When the abovetotal amount exceeds 5 mol %, a detrimental effect is caused on thedevitrification resistance, the transmittance, and the like.

[0064] Cs₂O has effects similar to the effects of K₂O. However, Cs₂O asa raw material is more expensive than Na₂O and K₂O, and increases thespecific gravity of the glass ceramic. The content of Cs₂O is thereforepreferably less than 1 mol %.

[0065] MgO can be used for improving the glass in meltability andadjusting the thermal expansion property of the glass ceramic. MgO isparticularly preferred since it can work to easily increase the thermalexpansion coefficient. However, MgO decreases the transmittance at andaround 400 nm and is liable to color the glass ceramic in brown. Thecontent of MgO is therefore preferably 0 to 3 mol %, particularlypreferably 0 to 1 mol %.

[0066] While CaO, SrO and BaO can be used for adjusting the thermalexpansion property of the glass ceramic, they are liable to form acoarse crystal and are liable to decrease the transmittance of the glassceramic. Particularly, SrO and BaO have the above tendency to a greatextent. Further, SrO and BaO are also liable to increase the specificgravity.

[0067] From the viewpoint of the prevention of coloring, particularly,the content of BaO is preferably 0.2 mol %, more preferably, 0.1 mol %or less, and it is desirable to incorporate no BaO.

[0068] The total content of CaO, SrO and BaO is preferably less than 3mol %. Further, it is desirable to incorporate no SrO like BaO.

[0069] ZnO is preferred for improving the meltability and maintainingthe transmittance. However, it is liable to increase the specificgravity. The content of ZnO is preferably 0 to 3 mol %, particularlypreferably 0 to 1 mol %.

[0070] From the viewpoint of the prevention of the coloring caused onthe glass ceramic by visible light scattering due to excess growth of acrystal phase (particularly, scattering on a shorter wavelength side),the content of P₂O₅ is preferably less than 0.1 mol %, more preferably0.05 mol % or less, and it is desirable to incorporate no P₂O₅. For thesame reason, the content of B₂O₃ is preferably less than 0.3 mol %, morepreferably less than 0.1 mol %, and it is desirable to incorporate noB₂O₃. In the present invention, the total content of Li₂O and the alkalimetal oxide is defined to be in the predetermined range, so that themeltability of the glass is not at all impaired even if the abovecomponents are decreased in content or omitted.

[0071] As₂O₃ is greatly limited in use since it is a harmful componentto human bodies. However, it is effective as a clarifier, and it isdesirably used in view of properties since it neither causes anydecrease in the transmittance of the glass ceramic nor causes anydecrease in homogeneity of the glass. Even when the content of As₂O₃exceeds 0.5 mol %, no further clarification effect can be obtained. Thecontent of As₂O₃ is therefore preferably 0.5 mol % or less, and it isfurther preferred to incorporate no As₂O₃. In a conventional matrixglass for a glass ceramic, As₂O₃ not only works as a clarifier but alsoworks to suppress coloring. A conventional matrix glass thereforecontains As₂O₃ although it is a toxic component. In the matrix glass ofthe present invention, the coloring of the glass ceramic can besuppressed even without incorporating As₂O₃, and the present inventiontherefore can accomplish a spectral transmittance in a visible lightregion and a high transmittance at a wavelength of 400 nm.

[0072] Sb₂O₃ is an effective component as a clarifier. However, when thecontent thereof is 0.1 mo % or more, the glass ceramic is liable to becolored, so that the content of Sb₂O₃ is preferably less than 0.1 mol %,more preferably 0.05 mol % or less. Since the glass ceramic of thepresent invention has a low melt viscosity, Sb₂O₃ can fully work as aclarifier even if the content thereof is 0.05 mol % or less.

[0073] SnO₂ also has a clarification effect. When the content thereof is0.1 mol % or more, the glass ceramic is liable to be colored, so thatthe content of SnO₂ is preferably less than 0.1 mol %, more preferably0.05 mol % or less, and it is desirable to incorporate no SnO₂.

[0074] SnO₃ is the most preferred as a clarifier. The effect of SO₃ as aclarifier has been known for a long time and has been widely used insoda lime glass. The present inventors have found that SO₃ is veryeffective for preventing the coloring of the glass ceramic and promotingthe melting of ZrO₂ in addition to the function thereof as a clarifierfor a glass. SO₃ can be introduced as a sulfate of a component to beincorporated. Particularly preferred is a sulfate of an alkali component(e.g., sodium sulfate, potassium sulfate or lithium sulfate) orzirconium sulfate. When Sb₂O₃ is used in a glass of this type, animmiscible layer may be generated in the surface of a molten glass.Further, the immiscible layer may catch a raw material for ZrO₂ and mayprevent the melting of ZrO₂, so that ZrO₂ remains non-melted in a finalproduct. SO₃ promotes the glass-forming reaction of raw materials, andunlike Sb₂O₃, SO₃ does not catch ZrO₂ within an immiscible layer toleave it non-melted. The content of SO₃ is preferably such that asulfate is introduced in an amount corresponding to at least 0.1 mol %but less than 3 mol % of an alkali component.

[0075] Other components may be incorporated so long as the object of thepresent invention is not impaired. Undesirably, however, the specificgravity is liable to be increased.

[0076] Further, the transmittance of the glass ceramic is decreased byexcess growth of a crystal phase or coloring components contained in thematrix glass. The coloring components are compounds or ions of Fe, V,Mn, Ni, Co, Cu, Ce, Cr, and the like. For obtaining the glass ceramicII-1 having a spectral transmittance of at least 70%, preferably a hightransmittance of at least 90%, in the entire visible light region (400nm to 750 nm) when the glass ceramic has a thickness of 5 mm, and forobtaining the glass ceramic II-2 having a high spectral transmittance ofat least 85% when it has a thickness of 1.1 mm, it is desirable toexclude the above components.

[0077] For the above reasons, it is determined that the matrix glass hasthe following composition. SiO₂ 55-70 mol % Al₂O₃ 13-23 mol % Totalcontent of alkali metal oxides 11-21 mol % Li₂O 10-20 mol % Totalcontent of Na₂O and K₂O 0.1-3 mol % TiO₂ 0.1-4 mol % ZrO₂ 0.1-2 mol %Total content of the above components at least 95 mol %

[0078] Further, for attaining a high transmittance in the entire visiblelight region (400 to 750 nm), the following components are limited incontent as below. BaO 0-less than 0.2 mol % P₂O₅ 0-less than 0.1 mol %B₂O₃ 0-less than 0.3 mol % SnO₂ 0-less than 0.1 mol %

[0079] Further, concerning the above composition, desirably, thecomposition contains none of iron oxide and a lead compound, contains noAs₂O₃, or contains none of SrO and BaO. More desirably, the compositioncontains none of iron oxide, a lead compound and As₂O₃, contains none ofiron oxide, a lead compound, SrO and BaO, or contains none of As₂O₃, SrOand BaO. Still more desirably, the composition contains none of ironoxide, a lead compound, As₂O₃, SrO and BaO. Further, SnO₂ has a smallclarification effect and colors the glass to a great extent, so that itis preferred to control the content thereof to be less than 0.1 mol %.More preferably, no SnO₂ is incorporated. Further, it is preferred toincorporate no CaO, for improving the devitrification resistance of thematrix glass during the production process thereof. Further, the contentof Sb₂O₃ is preferably 0.05 mol % or less, and more preferably zero.Further, it is preferred to use any raw materials in the form of asulfate.

[0080] The alkali metal oxide in the matrix glass is preferably a“two-components” combination of Li₂O as an essential component with Na₂Oor K₂O or a “three-components” combination of Li₂O, Na₂O and K₂O. Cs₂Ois expensive and increases the specific gravity, so that it is preferredto incorporate no Cs₂O.

[0081] The above composition may contain, as an optional component, 5mol % or less of at least one component selected from the groupconsisting of Cs₂O, MgO, CaO, SrO, BaO, ZnO, La₂O₃, Nb₂O₃, Y₂O₃, Bi₂O₃,WO₃, P₂O₅, B₂O₃, As₂O₃, Sb₂O₃, SnO₂, F and SO₃. These optionalcomponents are preferably contained in the form of oxides. When theabove optional components are added, it is preferred to incorporate ZnO,Sb₂O₃ or a combination of ZnO and Sb₂O₃.

[0082] The matrix glass for the glass ceramic is particularly preferablya composition comprising, by mol %, 63 to 68% of SiO₂, 15 to 20% ofAl₂O₃, 12 to 17% of Li₂O, 0.5 to 2% of Na₂O and K₂O in total, 1 to 3% ofTiO₂, 0.5 to 1.5% of ZrO₂, 1% or less of MgO, 1% or less of ZnO and lessthan 0.1% of Sb₂O₃. For preventing an increase in specific gravity, thematrix glass is further preferably a composition comprising the abovecomponents alone. In the above ranges of the components, preferably, thetotal content of Na₂O and K₂O is 1 to 2%.

[0083] A composition of glass raw materials that are prepared, thecomposition of the matrix glass and the composition of the glass ceramicare almost the same.

[0084] The method for producing the matrix glass of the presentinvention is not specially limited, and a conventional general methodcan be employed. For example, oxides, hydroxides, carbonates, nitrates,chlorides, sulfates, etc., are provided as glass raw materials asrequired, weighed to obtain a desired composition, and these rawmaterials are mixed to prepare a formulated raw material. The formulatedraw material is placed in a refractory crucible, melted at a temperatureof approximately 1,450 to 1,550° C., stirred and clarified to form ahomogeneous molten glass. For a matrix glass for a conventional glassceramic, the melting temperature is required to be approximately 1,600°C. or very high temperature. However, the above matrix glass in thepresent invention can be melted at a temperature of 1,550° C. or lower.It is because of the composition of the matrix glass that the glassceramic of the present invention is free from coloring exists in, and inaddition to this, that is also because impurities do not easily comefrom a container or a refractory furnace which the glass comes incontact with when melted, since the glass can be melted withoutemploying a high temperature of approximately 1,600° C. Such impuritiesalso contain a substance that colors the glass ceramic. The compositionof the matrix glass and the melting at a relatively low temperaturesuppress the coloring of the glass ceramic.

[0085] Then, the glass is cast into a mold to form a glass block, andthe glass block is transferred to a furnace that is heated to anannealing point of the glass, and cooled to room temperature.

[0086] The glass ceramics I and II of the present invention have acrystal phase containing a β-quartz solid solution precipitated by heattreatment of the above matrix glass for a glass ceramic. And, the glassceramic II-1 has a spectral transmittance of at least 70% at 400 to 750nm when it has a thickness of 5 mm.

[0087] The glass ceramic II-2 has a spectral transmittance of at least85% at 400 to 750 nm when it has a thickness of 1.1 mm.

[0088] The glass ceramics I and II of the present invention can becontrolled to have an average linear expansion coefficient of −10×10⁻⁷/°C. to +10×10⁻⁷/° C. in a temperature range of from 30° C. to 300° C.

[0089] The glass ceramic III-1 of the present invention is a glassceramic having a crystal phase containing a β-quartz solid solution,having a spectral transmittance of at least 70% at 400 to 750 nm when ithas a thickness of 5 mm, and having an average linear expansioncoefficient of from −10×10⁻⁷/° C. to +10×10⁻⁷/° C. in a temperaturerange of from 30° C. to 300° C. The glass ceramic III-2 of the presentinvention is a glass ceramic having a crystal phase containing aβ-quartz solid solution, having a spectral transmittance of at least 85%at 400 to 750 nm when it has a thickness of 1.1 mm, and having anaverage linear expansion coefficient of from −10×10⁻⁷/° C. to +10×10⁻⁷/°C. in a temperature range of from 30° C. to 300° C.

[0090] In the glass ceramic of the present invention, the term “crystalphase containing a β-quartz solid solution” refers to a crystal phasecontaining a β-quartz solid solution and/or a β-eucryptite solidsolution. Above all, a glass ceramic having crystal phases containing alargest volume of a β-quartz solid solution is preferred, and a glassceramic having a crystal phase formed of a β-quartz solid solution aloneis more preferred. Further, the volume of the crystal phase based on thetotal volume of the glass ceramic is generally at least 50%, and thecrystal phase generally has a size (average crystal grain size) of 5 to100 nm.

[0091] When the glass ceramic is used in a color display in which lightis transmitted through the glass ceramic, the transmittances towavelengths of three primary colors (wavelengths 435.8 nm, 546.1 nm and700 nm) are essential. Preferably, the transmittances to wavelengths ofthree primary colors are all at least 80%, more preferably at least 85%.Preferably, the glass ceramic of the present invention generally has atransmittance of at least 80% at 430 nm, and transmittances of at least80% to all of wavelengths of three primary colors, when it has athickness of 5 mm.

[0092] Further, the glass ceramic of the present invention generally hasa transmittance of at least 85% at 430 nm, and transmittances of atleast 85% to all of wavelengths of three primary colors, when it has athickness of 1.1 mm.

[0093] Not only the glass ceramic of the present invention has a hightransmittance in a visible light region, but also the start pointthereof in an ultraviolet region shifts toward a shorter wavelength sideas compared with a conventional glass ceramic. This is presumablybecause the crystallization rate of the glass ceramic is controlled sothat crystal grain sizes of the β-quartz solid solution to beprecipitated can be controlled to be small and uniform. The glassceramic of the present invention has a transmittance of approximately atleast 70% to light having a wavelength of 365 nm when it has a thicknessof 1 mm, which light is useful for ultraviolet curing, so that the glassceramic can be supplied with ultraviolet light sufficient forultraviolet curing. Therefore, an ultraviolet-curing resin can beeffectively used, so that the time period required in a bonding step canbe decreased to a great extent and that the production cost in broadfields including the field of a liquid crystal projector can bedecreased.

[0094] The glass ceramic of the present invention has an average linearexpansion coefficient of −10×10⁻⁷/° C. to +10×10⁻⁷/° C. at a temperaturein the range of from 30 to 300° C., and has a high transmittance in theabove visible light region, and the volume change thereof caused bythermal expansion is small in a broad temperature range. Further, theglass ceramic of the present invention is also excellent in heat shockresistance. Therefore, it can be used as a substitute as a quartz glassand, at the same time, produces effect that it does not easily caused toundergo distortion or deformation by thermal expansion or shrinkage whenbonded to a quartz glass. The average linear expansion coefficient inthe above temperature range is preferably −5×10⁻⁷/° C. to +5×10⁻⁷/° C.,more preferably −2×10⁻⁷/° C. to +2×10⁻⁷/° C. When the glass ceramic ofthe present invention is used as a dustproof substrate for a liquidcrystal projector or as a substrate opposite to a substrate with a thinfilm transistor in a liquid crystal panel, desirably, the average linearexpansion coefficient of the glass ceramic in environments of use of theliquid crystal projector and temperature environments (300 to 150° C.)in the production process thereof is −10×10⁻⁷/° C. to +10×10⁻⁷/° C.,preferably −5×10⁻⁷/° C. to +5×10⁻⁷/° C., more preferably −2×10⁻⁷/° C. to+2×10⁻⁷/° C.

[0095] The glass ceramic of the present invention can have a specificgravity of 2.2 or more but less than 2.5, or has a low specific gravity.Most of conventional transparent glass ceramics have a specific gravityof 2.5 or more, and a quartz glass has a specific gravity of 2.2, sothat such a large specific gravity was a large barrier against use as asubstitute for the quartz glass. In contrast, the glass ceramic of thepresent invention has a specific gravity similar to that of a quartzglass and is advantageous for use as a substitute for the quartz glass.

[0096] The glass ceramic of the present invention can be produced, forexample, by the following method.

[0097] A block of the above matrix glass for a glass ceramic is cut asrequired and heated up to a temperature of 750° C. or higher from roomtemperature, to carry out crystallization. In the crystallization, therecan be employed a method of gradually increasing a temperature, orincreasing a temperature stepwise, from room temperature toapproximately 950° C. Preferably, there is employed a “two-steps” heattreatment method in which a cut block of the matrix glass is held at atemperature of 650 to 750° C. for approximately 30 minutes to 2 hours,the temperature is increased to 800 to 950° C., and the cut block isheld at 800 to 950° C. for approximately 30 minutes to 2 hours. Thetemperature elevation rate is preferably 50-300° C./hour. As comparedwith any conventional glass ceramic, the crystallization step can becarried out for a short period of time.

[0098] Alternatively, a molten glass is formed into a thin sheet glassto obtain a matrix glass, the matrix glass is subjected to thecrystallization treatment, and then the main surface(s) of the glassceramic is cut and polished, or the main surface(s) of matrix glass iscut and polished and then subjected to the crystallization treatment, toobtain a glass ceramic substrate. The thus-obtained glass ceramicsubstrate exhibits a high transmittance in a visible light region, has alight weight and low thermal expansion properties and also has chemicalstability. The thus-obtained substrate can be used as a substrate for adisplay, particularly, a substrate that is opposite to a polysiliconliquid crystal display substrate and constitutes a liquid crystaldisplay (TFT opposite substrate), a dustproof substrate for a liquidcrystal projector, a substrate for a reflection mirror of anastronomical telescope or a semiconductor aligner, a diffractiongrating, a substrate for an information recording medium, a surfaceplate, or the like.

[0099] A transparent electrically conductive film may be formed on theTFT opposite substrate as required, or an anti-reflection film may beformed on the dustproof substrate for a liquid crystal projector.

[0100] The above glass ceramic can be also used as a substitute for aquartz glass, a measurement standard, or a part of a laser oscillator ora laser gyroscope.

[0101] The use of the glass ceramic of the present invention as anopposite substrate and a dustproof substrate for a liquid crystal panelwill be explained below. Generally, the liquid crystal panel for use ina liquid crystal display has a liquid crystal layer, a driving substratethat is arranged to face an opposite substrate with the liquid crystallayer between them and is for holding and driving the liquid crystallayer, and an opposite substrate. The driving substrate has a substrate,a pixel electrode provided on the substrate and a switching elementconnected to the pixel electrode. The opposite substrate has alight-transmitting substrate and an opposite electrode provided in aposition of the light-transmitting substrate which position faces thepixel electrode. The liquid crystal layer is held between the drivingsubstrate and the opposite substrate through an alignment film, and isdriven by voltage applied between the pixel electrode and the oppositeelectrode.

[0102] In the above constitution, the transmittance of light that comesfrom the opposite substrate side is controlled in each pixel on thebasis of alignment of the liquid crystal layer controlled with the abovepixel electrode and the opposite electrode, and the light forms animage. In some liquid crystal panels of the above type, alight-transmitting substrate having a predetermined thickness isattached to an outside of at least one of the driving substrate or theopposite substrate for heat radiation and for preventing deteriorationof the image caused when dust adheres to the liquid crystal panel. Theglass ceramic of the present invention can be suitably used as anopposite substrate and a dustproof substrate of the above liquid crystalpanel.

[0103]FIG. 1 schematically shows one example of structure of a liquidcrystal panel having a dustproof substrate. In the present invention,the glass ceramic substrate of the present invention is used as alight-transmitting substrate of an opposite substrate 2 of a liquidcrystal panel 1, or as transparent substrates 14 a and 14 b of dustproofsubstrates 4 a and 4 b.

[0104] The opposite substrate 2 to which the glass ceramic substrate ofthe present invention is applied will be explained.

[0105] The opposite substrate 2 has a structure in which an oppositeelectrode 20 is formed on a light-transmitting substrate 13 made of theglass ceramic of the present invention. Further, a light-shielding layer19 for preventing the incidence of light to switching elements 17 formedon a driving substrate is formed in a position facing the switchingelement 17. The light-shielding layer 19 is formed in a matrix form.

[0106] Generally, the above light-shielding layer 19 can be formed ofany material that works as a shield against the incidence of light. Thelight-shielding layer is preferably a high-reflection film formed on thelight incidence side for preventing a malfunction caused on a liquidcrystal panel by heat absorbed in the light-shielding layer. Forpreventing a crosstalk in the liquid crystal layer, the light-shieldinglayer is preferably a low-reflection film on the driving substrate side.More preferably, the light-shielding layer 19 is a stack of films one ofwhich is a high-reflection film on the light incidence side and theother of which is a low-reflection film on the driving substrate side.The light-shielding layer 19 is formed on the light-transmittingsubstrate 13 by a known photolithography method or the like.

[0107] An opposite electrode 20 formed on the light-transmittingsubstrate 13 is for controlling the alignment of a liquid crystal layer15 together with a pixel electrode 16 of the driving substrate 3. Theopposite electrode 20 is formed from a material transparent to theincidence of light. For example, the material includes a transparentelectrically conductive film, and for visible light, an ITO film isformed by a known method.

[0108] For effective incidence of light to a pixel region, a substratehaving a microlens array may be provided before the opposite substrate(on the light incidence side). Further, a color filter may be formed onthe opposite substrate as required, and in this case, color display canbe made.

[0109] The dustproof substrates 4 a and 4 b made of the glass ceramic ofthe present invention each will be explained below. The dustproofsubstrate 4 a or 4 b is boned to an outside of the opposite substrate 2or the driving substrate 3 for preventing a degradation of imagequalities caused by dust adhering to the opposite substrate 2 or thedriving substrate 3. The dustproof substrates 4 a and 4 b have astructure in which an anti-reflection film 21 a or 21 b is formed on atransparent substrate 14 a or 14 b made of the glass ceramic of thepresent invention.

[0110] When the dustproof substrate 4 a is provided to an outside of theopposite substrate 2, an anti-reflection film 21 a is formed on thelight incidence side of the dustproof substrate 4 a. When the dustproofsubstrate 4 b is provided to an outside of the driving substrate 3, ananti-reflection film 21 b is formed on the light exit side. Theanti-reflection films 21 a and 21 b can be selected from films havinganti-reflection properties to the incidence of light to be employed, andfor example, when visible light is employed, an alternately stacked filmof TiO₂ and SiO₂ is known. The anti-reflection films 21 a and 21 b canbe formed on the transparent substrates 14 a and 14 b by a known methodsuch as a sputtering method, a vapor deposition method, or the like.

[0111] The dustproof substrate 4 a or 4 b is preferably bonded to theopposite substrate 2 or the driving substrate 3 with an adhesive such asan ultraviolet-curable resin. The glass ceramic substrate of the presentinvention has excellent transmittance to light at and around 365 nmuseful for ultraviolet curing as compared with a conventional glassceramic substrate, so that the bonding with an ultraviolet-curable resincan be performed.

[0112] The dustproof substrates 4 a and 4 b may be provided to outsidesof the opposite substrate 2 and the driving substrate 3, or one of thedustproof substrates may be provided to one side. For preventing theincidence of light to a wiring provided for driving the switchingelement of the driving substrate 3, a light-shielding layer having apredetermined width may be formed in a circumferential region of thedustproof substrate.

[0113] As explained above, the glass ceramic substrate of the presentinvention can be used as an opposite substrate for a liquid crystalpanel or a light-transmitting substrate for a dustproof substrate.

[0114] According to the present invention, there is also provided adustproof substrate for a liquid crystal panel, which dustproofsubstrate uses, as a transparent substrate, the glass ceramic substratehaving a spectral transmittance of at least 70% at 400 to 750 nm whenthe glass ceramic substrate has a thickness of 5 mm and/or a spectraltransmittance of at least 85% at 400 to 750 nm when it has a thicknessof 1.1 mm. The above glass ceramic substrate preferably has a crystalphase containing a β-quartz solid solution and having an average linearexpansion coefficient of −5×10⁻⁷/° C. to +5×10⁻⁷/° C. at a temperaturein the range of from 30 to 300° C., and preferably has a specificgravity of 2.2 or more but lass than 2.5.

[0115] The glass ceramic of the present invention has excellenttransmittance in a visible light region, particularly, in a shortwavelength region as compared with any conventional glass ceramic, sothat the influence of coloring of images formed by a liquid crystalpanel can be decreased. Further, since the glass ceramic of the presentinvention has a smaller specific gravity than any conventional glassceramic, it is advantageous for decreasing the weight of a liquidcrystal panel. Further, since the glass ceramic of the present inventioncan be produced with good productivity, substrates can be produced at alower cost. In view of the above points, the glass ceramic of thepresent invention can be substituted for a conventional quartz glass assubstrate(s) for a liquid crystal panel, and is useful for decreasingthe cost of the liquid crystal panel.

[0116] As explained above, the opposite substrate and the dustproofsubstrate made of the glass ceramic of the present invention each can besuitably employed in a liquid crystal panel of a liquid crystal displayor a liquid crystal projector.

EXAMPLES

[0117] The present invention will be explained further in detail withreference to Examples hereinafter, while the present invention shall notbe limited by these Examples.

Examples 1-10 and Comparative Examples 1-3

[0118] Oxides, hydroxides, carbonates, nitrates, chlorides, sulfates,etc., were weighed and mixed to obtain compositions as shown in Tables 1to 3, whereby batch raw materials were prepared. For clarifying andpromoting melting of glasses and preventing coloring of the glasses,Na₂O, K₂O and Li₂O were used up to a total amount of 0.5 to 2 mol % inthe form of sulfates. The sulfates were decomposed and volatilized inthe steps of melting under heat and clarification, so that almost nosulfates remained in the glasses obtained. Tables 1 to 3 therefore donot have any particular description of SO₃.

[0119] In each Example, the above-formulated raw material was placed ina platinum crucible, heated to 1,450 to 1,550° C., melted, stirred,homogenized and clarified, and a molten glass is cast into a mold. Afterthe glass was solidified, the glass was transferred to an electricfurnace that had been heated approximately to an annealing point of theglass, to cool the glass to room temperature.

[0120] A glass having a size of approximately 300×300×2 mm was preparedfrom the above-obtained glass block by cutting, and heated in anelectric furnace to crystallize the glass, whereby a glass ceramic wasobtained. The crystallization was carried out by holding the glass attwo stages for, a first holding temperature and a second holdingtemperature as shown in Tables 1 to 3, a predetermined period of timeeach. The temperature elevation rate up to the first holding temperaturewas 200° C./hour, and the temperature elevation rate from the firstholding temperature to the second holding temperature was 60° C./hour.

[0121] The thus-obtained glass ceramics were measured for physicalproperties and subjected to X-ray diffraction of precipitated crystalphases. Tables 1 to 3 show the results.

[0122] (1) Average linear expansion coefficient

[0123] An average linear expansion coefficient in the temperature rangeof from 30 to 300° C. was calculated on the basis of values obtained bymeasurement with a thermomechanical analyzer (TMA). (Japan Optical GlassIndustry Society Standard was employed, and average linear expansioncoefficients obtained by modifying data in the temperature range of from100 to 300° C. to data in the temperature range of from 30 to 300° C.were used).

[0124] (2) Spectral transmittance

[0125] A glass ceramic, both surfaces of which were polished to attain athickness of 2 mm, was measured with a spectrophotometer.

[0126] (3) Specific gravity

[0127] Measured with a densitometer according to Japan Optical GlassIndustry Society Standard.

[0128] (4) Size of precipitated crystal phase (average crystal graindiameter)

[0129] An electron microscope was used to measure sizes of precipitatedcrystal phases (to determine an average crystal grain diameter).

[0130] Each of glass ceramics obtained in all the Examples had aspectral transmittance of 70% or more at a wavelength of 400 to 750 nmwhen the value thereof was converted to a value to be obtained when theyhad a thickness of 5 mm. Further, each of the glass ceramics obtained inall the Examples had a spectral transmittance of 85% or more at awavelength of 400 to 750 nm when the value thereof was converted to avalue to be obtained when they had a thickness of 1.1 mm. The volume ofthe precipitated crystal glass in the glass ceramics is 50% or more.TABLE 1 Example 1 2 3 4 5 Glass Composition SiO₂ 62.9 67.0 63.0 63.064.3 Al₂O₃ 17.0 16.6 21.0 16.8 17.0 Li₂O 16.0 12.0 12.0 16.0 13.5 Na₂O0.0 0.0 0.0 1.0 0.0 K₂O 1.0 1.0 1.0 0.0 1.0 MgO 0.0 0.0 0.0 0.0 0.0 ZnO0.0 0.0 0.0 0.0 1.0 TiO₂ 2.0 2.0 2.0 2.0 2.0 ZrO₂ 1.0 1.0 1.0 1.0 1.0Sb₂O₃ 0.00 0.00 0.02 0.00 0.00 As₂O₃ 0.10 0.40 0.00 0.20 0.20 Na₂O + K₂O1.00 1.00 1.00 1.00 1.00 TAMO* 17.0 13.0 13.0 17.0 14.5 Total 100.0100.0 100.0 100.0 100.0 First Holding Temperature (° C.) 680 700 700 720700 Time (h) 1 1 0.5 1 1 Second Holding Temperature (° C.) 800 850 820850 850 Time (h) 1 1 1 0.5 1 Crystal phase precipitated β-q β-q β-q β-qβ-q Average linear expansion −7.1 −5.7 −1.0 −10.0 0.2 coefficientα30-300 (×10⁻⁷/° C.) Specific gravity 2.44 2.45 2.46 2.44 2.47Transmittance at 400 nm (%) at thickness 72 79 75 75 76 of 5 mm atthickness 86 88 87 87 87 of 1.1 mm Size of precipitated crystal 50 20 3030 50 phase (average crystal grain diameter) (nm)

[0131] TABLE 2 Example 6 7 8 9 10 Glass Composition SiO₂ 64.0 65.8 65.866.0 65.0 Al₂O₃ 16.5 17.0 16.5 17.0 17.0 Li₂O 14.5 13.0 11.7 12.0 14.0Na₂O 1.0 0.0 2.0 0.0 0.0 K₂O 1.0 1.0 0.0 1.0 1.0 MgO 0.0 0.0 1.0 1.0 0.0ZnO 0.0 0.0 0.0 0.0 0.0 TiO₂ 2.0 2.4 2.0 2.0 2.0 ZrO₂ 1.0 0.6 1.0 1.01.0 Sb₂O₃ 0.02 0.00 0.02 0.02 0.00 As₂O₃ 0.00 0.20 0.00 0.00 0.00 Na₂O +K₂O 2.00 1.00 2.00 1.00 1.00 TAMO* 16.5 14.0 13.7 13.0 15.0 Total 100.0100.0 100.0 100.0 100.0 First Holding Temperature (° C.) 720 700 700 650700 Time (h) 1 1 1 2 2 Second Holding Temperature (° C.) 820 850 830 850850 Time (h) 1 1 2 2 2 Crystal phase precipitated β-q β-q β-q β-q β-qAverage linear expansion coefficient 1.0 4.5 0.0 −2.0 −4.6 α30-300(×10⁻⁷/° C.) Specific gravity 2.44 2.45 2.47 2.48 2.45 Transmittance at400 nm (%) at thickness 71 72 74 76 78 of 5 mm at thickness 85 86 87 8788 of 1.1 mm Size of precipitated crystal 50 50 40 30 20 phase (averagecrystal grain diameter) (nm)

[0132] TABLE 3 Comparative Example 1 2 3 Glass Composition SiO₂ 63.864.9 70.9 Al₂O₃ 17.1 16.3 14.5 Li₂O 8.5 10.1 9.2 Na₂O 0.6 0.0 0.6 K₂O0.0 0.0 0.2 MgO 1.7 4.1 0.8 ZnO 1.2 1.0 0.0 P₂O₅ 3.8 0.0 0.6 TiO₂ 2.02.1 1.6 ZrO₂ 1.1 1.1 1.2 Sb₂O₃ 0.00 0.40 0.00 As₂O₃ 0.20 0.00 0.40Na₂O + K₂O 0.60 0.00 0.80 TAMO* 9.1 10.1 10.0 Total 100.0 100.0 100.0First Holding Temperature (° C.) 800 700 700 Time (h) 24 10 2 SecondHolding Temperature (° C.) 820 850 Time (h) 10 1 Crystal phaseprecipitated β-q β-q β-q Average linear expansion 0.0 10.0 −7.2coefficient α30-300 (×10⁻⁷/° C.) Specific gravity 2.53 2.57 2.51Transmittance at 400 nm (%) at thickness 64 56 61 of 5 mm at thickness82 75 80 of 1.1 mm Size of precipitated crystal 30 50 30 phase (averagecrystal grain diameter) (nm)

[0133] Notes to Tables 1 to 3:

[0134] 1) “β-q” refers to a β-quartz solid solution.

[0135] 2) Concerning any contents of components other than less than 0.1mol % of any component, the contents thereof were rounded of to onedecimal place.

[0136] Both surfaces of the glass ceramic plates obtained in Examplesare cut and polished, to give glass ceramic substrates. When dimensionsof the glass ceramic substrate are determined depending upon use, thethus-obtained substrate can be used as a substrate for a display,particularly, a TFT opposite substrate, a dustproof substrate for aliquid crystal projector, a substrate for a reflection mirror of anastronomical telescope or a semiconductor aligner, a diffractiongrating, a substrate for an information recording medium, a surfaceplate, or the like.

[0137] The above glass ceramic can be also used as a substitute for aquartz glass, a measurement standard, or a part of a laser oscillator ora laser gyroscope.

Example 11

[0138] Example 11 shows examples in which the glass ceramics obtained inExamples 1 to 10 were used for making opposite substrates for use in aliquid crystal panel of a liquid crystal projector.

[0139]FIG. 2 schematically shows an opposite substrate 30 in thisExample. The opposite substrate 30 is structured by forming an oppositeelectrode 32 on a light-transmitting substrate 31 made of the glassceramic of the present invention.

[0140] First, both main surfaces of the glass ceramic plate obtained inany one of Examples 1 to 10 were cut and polished, and then the glassceramic plate was cut to obtain a glass substrate having a size of 200mm×200 mm and a thickness of 1.1 mm.

[0141] Then, an ITO film having a thickness of 140 nm, which was toconstitute an opposite electrode for driving a liquid crystal, wasformed on one surface of the glass substrate. The ITO film was formed bya sputtering method. The obtained ITO film had a sheet resistance of 20Ω/□.

[0142] Further, the glass substrate having the ITO film formed thereonwas cut to a size of 20 mm×18 mm.

[0143] In this manner, opposite substrates 30 for liquid crystal panelsin this Example were obtained, in each of which the ITO film 32 wasformed on the substrate 31.

[0144] The opposite substrates for a liquid crystal panel, obtained inthis Example, were used to fabricate liquid crystal panels for aprojection type liquid crystal projector. When any one of the glassceramics obtained in Examples 1 to 10 was used, less colored andexcellent images were obtained. It has been found that the oppositesubstrate for a liquid crystal panel, made of the glass ceramic of thepresent invention, can be used as a substitute for a conventionalopposite substrate made of quartz.

Example 12

[0145] Example 12 shows examples in which the glass ceramics obtained inExamples 1 to 10 were similarly used for making opposite substrates foruse in a liquid crystal panel of a liquid crystal projector. Example 12differs from Example 11 in that, in this Example 12, a pattern oflight-shielding layer (black matrix) for preventing the incidence oflight into a switching element such as TFT formed on a driving substratewas formed on a light-transmitting substrate made of the glass ceramicof the present invention.

[0146] FIGS. 3(a) to 3(d) schematically show the steps of producing theopposite substrate in this Example.

[0147] Like Example 11, a glass substrate 41 having a size of 200 mm×200mm and a thickness of 1.1 mm was obtained from one of the glass ceramicplates obtained in Examples 1 to 10.

[0148] Then, a light-shielding layer 42 having a thickness of 100 nm wasformed on one surface of the glass substrate 41 (FIG. 3 (a)). Thelight-shielding layer 42 had the laminated structure of two layers, onelayer being a high-reflection film that was formed on the glasssubstrate side and had high-reflection to the incidence of light, theother layer being a low-reflection film formed on the liquid crystalside. This Example used an aluminum layer as a high-reflection film, anda chromium nitride layer as a low-reflection film.

[0149] The above light-shielding layer 42 was formed by a sputteringmethod. Specifically, as a target material, there was used a targetmaterial that had a width of 15 cm and was made of aluminum covering awidth of 5 cm on the substrate entrance side and of chromium covering awidth of 10 cm on the substrate exit side, and the target wascontinuously sputtered with an inline sputtering apparatus, to form thelayer. Further, when the chromium nitride layer was formed, argon gascontaining nitrogen was allowed to flow from the substrate exit side.

[0150] In the above manner, an aluminum thin film having a thickness of20 nm was formed on the glass substrate 41, and a chromium nitride thinfilm having a thickness of 80 nm was formed thereon. In this case, amixture region containing aluminum and chromium nitride was formed in aninterface between the aluminum thin film and the chromium nitride thinfilm. In the mixture region, the aluminum concentration continuouslydecreased from the glass substrate side to the chromium nitride layerside.

[0151] Then, a predetermined pattern 44 was formed on thelight-shielding layer 42 formed. The pattern 44 of the light-shieldinglayer 42 was formed in a position where the light-shielding layer 42prevents the incidence of light to a switching element of the drivingsubstrate provided so as to face the opposite substrate with a liquidcrystal layer between them.

[0152] First, a photosensitive layer (resist) 43 having a thickness of500 nm was formed on the chromium nitride film of the light-shieldinglayer 42 (FIG. 3(b)). Further, the resist layer was formed in a matrixform having a width of 4 μm and a pitch of 26 μm with using a photomask.

[0153] Then, the substrate having the formed resist layer in the matrixform was immersed in a chromium etching solution (HY solution, suppliedby Wako Purechemical K.K.) to etch the chromium nitride thin film inaccordance with the formed resist pattern, whereby a pattern was formedin the chromium nitride thin film. Then, the above substrate wasimmersed in an alkaline aqueous solution as a solution for removing theresist, to remove the resist layer and, at the same time, to etch thealuminum thin film, whereby a pattern according to the chromium nitridethin film pattern was formed in the aluminum thin film. In this manner,a light-shielding pattern 44 was formed in the light-shielding layer 42(FIG. 3(c)).

[0154] Then, an ITO film 45 having a thickness of 140 nm, which was anopposite electrode as a liquid crystal driving electrode, was formed onthe glass substrate so as to cover the light-shielding pattern 44 (FIG.3(d)).

[0155] The ITO film was formed by a sputtering method. The thus-obtainedITO film 45 had a sheet resistance of 25 Ω/□.

[0156] Further, the glass substrate 41 having the formed light-shieldingpattern 44 and the formed ITO film 45 was cut to a size of 20 mm×18 mm.

[0157] In the above manner, the opposite substrates for liquid crystalpanels were obtained in this Example.

[0158] The opposite substrates for a liquid crystal panel, obtained inthis Example, were used to fabricate liquid crystal panels for aprojection type liquid crystal projector. When any one of the glassceramics obtained in Examples 1 to 10 was used, less colored andexcellent images were obtained. It has been found that the oppositesubstrate for a liquid crystal panel, made of the glass ceramic of thepresent invention, can be used as a substitute for a conventionalopposite substrate made of quartz.

Example 13

[0159] Example 13 shows examples in which the glass ceramic of thepresent invention was used to fabricate a dustproof substrate for use ina liquid crystal panel of a liquid crystal projector.

[0160]FIG. 4 schematically shows a dustproof substrate 50 of thisExample.

[0161] First, two main surfaces of each of the glass ceramic platesobtained in Examples 1 to 10, as transparent substrates, were cut andpolished, and then the glass substrate plates were cut to obtain glasssubstrates having a size of 200 mm×200 mm and a thickness of 1.1 mmeach.

[0162] Then, an anti-reflection film to visible light (wavelength430-650 nm) was formed on one surface of each glass substrate. Eachanti-reflection film had a three-layered structure in which an aluminumoxide (Al₂O₃) layer, a zirconium oxide (ZrO₂) layer and a magnesiumfluoride (MgF₂) layer were laminated in this order from the glasssubstrate side. The above-formed layers had a thickness of approximately83 nm, approximately 132 nm and approximately 98 nm.

[0163] The above anti-reflection films were formed by consecutive vacuumdeposition of materials for the layers.

[0164] The substrate having the above anti-reflection films formedthereon had a transmittance of 96% or more to visible light (wavelength430-650 nm) and a reflectance of 0.6% or lower.

[0165] Then, the glass substrates having the anti-reflection filmsformed thereon were cut to a size of 25 mm×18 mm.

[0166] In the above manner, dustproof substrates 50 of this Examplehaving the anti-reflection films 52 formed on the transparent substrate51 were obtained.

[0167] The dustproof substrates 50 for a liquid crystal panel, obtainedin this Example, were used to fabricate liquid crystal panels for aprojection type liquid crystal projector. In each case, the dustproofsubstrates were bonded to outsides of the opposite substrate and thedriving substrate, and an ultraviolet-curable resin was used for thebonding. Since the ultraviolet-curable resin was used, the time periodfor the bonding step was greatly decreased as compared with a case wherea conventional heat-curable resin was used for bonding.

[0168] When any one of the glass ceramics obtained in Examples 1 to 10was used for fabricating the above liquid crystal panel, less coloredand excellent images were obtained. It has been found that the dustproofsubstrate made of the glass ceramic of the present invention can be usedas a substitute for a dustproof substrate made of quartz.

[0169] In addition, the opposite substrate and the dustproof substratemade of the glass ceramic of the present invention can be also appliedto reflection type liquid crystal panels of reflection type projector,and the like.

EFFECT OF THE INVENTION

[0170] The matrix glass for the glass ceramic of the present inventionhas a relatively low melting temperature, so that a remarkablyhomogeneous matrix glass can be obtained with a melting furnace for ageneral optical glass. Further, it has a composition that is not easilycolored, and moreover, impurities that will cause coloring do not easilycome from a container or a refractory furnace during melting thereof, sothat the glass ceramic of the present invention having a high spectraltransmittance, low thermal expansion properties and a small specificgravity can be produced by carrying out crystallization treatment for arelatively short period of time.

[0171] Further, since the glass ceramic of the present invention has ahigh spectral transmittance in a visible light region, low thermalexpansion properties and a small specific gravity, it can be used as asubstitute material for an expensive quartz glass. Further, since it hasa low thermal expansion coefficient, it can give a material excellent inheat shock resistance.

[0172] Furthermore, since the glass ceramic substrate of the presentinvention has the above glass ceramic as a substrate material, it hasfeatures such as transparency, low thermal expansion and being light inweight, so that it can be suitably used in various fields including adustproof substrate for a liquid crystal projector, and the like.

[0173] Moreover, the opposite substrate and the dustproof substrate fora liquid crystal panel, which comprise the glass ceramic substrate ofthe present invention, have a light weight and are thereforeadvantageous for decreasing the weight of a liquid crystal panel.Further, the glass ceramic itself has excellent productivity, so that itcan be produced at a low cost.

What is claimed is:
 1. A glass ceramic having a crystal phase containinga β-quartz solid solution precipitated by heat treatment of a matrixglass for a glass ceramic, the matrix glass having a glass compositioncomprising 55 to 70 mol % of SiO₂, 13 to 23 mol % of Al₂O₃, 11 to 21 mol% of an alkali metal oxide, provided that the alkali metal oxidecontains 10 to 20 mol % of Li₂O and contains 0.1 to 3 mol % of Na₂O andK₂O in total, 0.1 to 4 mol % of TiO₂ and 0.1 to 2 mol % of ZrO₂, thetotal content of said components being at least 95 mol %, and furthercomprising 0 to less than 0.2 mol % of BaO, 0 to less than 0.1 mol % ofP₂O₅, 0 to less than 0.3 mol % of B₂O₃ and 0 to leas than 0.1 mol % ofSnO₂.
 2. The glass ceramic of claim 1, wherein the glass matrix containsat least one component selected from the group consisting of Cs₂O, MgO,CaO, SrO, ZnO, La₂O₃, Nb₂O₅, Y₂O₃, Bi₂O₃, WO₃, As₂O₃, Sb₂O₃, F and SO₃,and the total content of the at least one component selected from saidgroup and BaO, P₂O₅, B₂O₃ and SnO₂ is 5 mol % or less.
 3. A glassceramic having a crystal phase containing a β-quartz solid solutionprecipitated by heat treatment of a matrix glass for a glass ceramic andhaving a spectral transmittance of at least 70% at 400 to 750 nm when ithas a thickness of 5 mm, the matrix glass having a glass compositioncomprising 55 to 70 mol % of SiO₂, 13 to 23 mol % of Al₂O₃, 11 to 21 mol% of alkali metal oxides, provided that the content of Li₂O is 10 to 20mol % and that the total content of Na₂O and K₂O is 0.1 to 3 mol %, 0.1to 4 mol % of TiO₂ and 0.1 to 2 mol % of ZrO₂, the total content of saidcomponents being at least 95 mol %.
 4. A glass ceramic having a crystalphase containing a β-quartz solid solution precipitated by heattreatment of a matrix glass for a glass ceramic and having a spectraltransmittance of at least 85% at 400 to 750 nm when it has a thicknessof 1.1 mm, the matrix glass having a glass composition comprising 55 to70 mol % of SiO₂, 13 to 23 mol % of Al₂O₃, 11 to 21 mol % of an alkalimetal oxide, provided that the alkali metal oxide contains 10 to 20 mol% of Li₂O and contains 0.1 to 3 mol % of Na₂O and K₂O in total, 0.1 to 4mol % of TiO₂ and 0.1 to 2 mol % of ZrO₂, the total content of saidcomponents being at least 95 mol %.
 5. The glass ceramic of claim 3 or4, wherein the matrix glass contains 5 mol % or less of at least onecomponent selected from the group consisting of Cs₂O, MgO, CaO, SrO,BaO, ZnO, La₂O₃, Nb₂O₅, Y₂O₃, Bi₂O₃, WO₃, P₂O₅, B₂O₃, As₂O₃, Sb₂O₃,SnO₂, F and SO₃.
 6. The glass ceramic of any one of claims 1 to 5, whichhas an average linear expansion coefficient of from −10×10⁻⁷/° C. to+10×10⁻⁷/° C. in a temperature range of from 30° C. to 300° C.
 7. Aglass ceramic having a crystal phase containing a β-quartz solidsolution, having a spectral transmittance of at least 70% at 400 to 750nm when it has a thickness of 5 mm, and having an average linearexpansion coefficient of from −10×10⁻⁷/° C. to +10×10⁻⁷/° C. in atemperature range of from 30° C. to 300° C.
 8. A glass ceramic having acrystal phase containing a β-quartz solid solution, having a spectraltransmittance of at least 85% at 400 to 750 nm when it has a thicknessof 1.1 mm, and having an average linear expansion coefficient of from−10×10⁻⁷/° C. to +10×10⁻⁷/° C. in a temperature range of from 30° C. to300° C.
 9. The glass ceramic of any one of claims 1 to 8, wherein thecrystal phase has a volume of at least 50% based on the total volume ofthe glass ceramic.
 10. The glass ceramic of any one of claims 1 to 9,wherein the crystal phase has an average crystal grain size of 5 to 100nm.
 11. The glass ceramic of any one of claims 1 to 10, which has aspecific gravity of 2.2 or more but less than 2.5.
 12. A glass ceramicsubstrate comprising the glass ceramic of any one of claims 1 to
 11. 13.An opposite substrate for use in a liquid crystal panel having alight-transmitting substrate and an opposite electrode formed thereon,the light-transmitting substrate being the glass ceramic substrate ofclaim
 12. 14. The opposite substrate of claim 13, wherein the liquidcrystal panel has (a) a driving substrate having a substrate, a pixelelectrode formed on said substrate and a switching element connected tosaid pixel electrode, (b) an opposite substrate that is positionedopposite to said driving substrate through a predetermined space and hasa light-transmitting substrate and an opposite electrode in a positionbeing on said light-transmitting substrate and facing said pixelelectrode, and (c) a liquid crystal layer which is held in apredetermined space formed between said driving substrate and a drivingsubstrate and is drivable by a voltage upon application of the voltagebetween said pixel electrode and the opposite electrode.
 15. Theopposite substrate of claim 14, which further has a light-shielding filmformed in a position that is opposite to the switching element of thedriving substrate and is on the light-transmitting substrate.
 16. Adustproof substrate for a liquid crystal panel having a transparentsubstrate and an anti-reflection film formed thereon, the transparentsubstrate being the glass ceramic substrate of claim
 12. 17. A dustproofsubstrate for a liquid crystal panel having a transparent substrate andan anti-reflection film formed thereon, the transparent substrate beinga glass ceramic substrate which has a spectral transmittance of at least70% at 400 to 750 nm when it has a thickness of 5 mm.
 18. A dustproofsubstrate for a liquid crystal panel having a transparent substrate andan anti-reflection film formed thereon, the transparent substrate beingmade of a glass ceramic substrate which has a spectral transmittance ofat least 85% at 400 to 750 nm when it has a thickness of 1.1 mm.
 19. Thedustproof substrate of claim 17, 18 or 19, wherein the glass ceramicsubstrate has a crystal phase containing a β-quartz solid solution andhas an average linear expansion coefficient of from −5×10⁻⁷/° C. to+5×10⁻⁷/° C. in a temperature range of from 30° C. to 300° C.
 20. Thedustproof substrate as recited of claim 17 or 18 wherein the glassceramic substrate has a specific gravity of at least 2.2 but less than2.5.
 21. The dust proof substrate of any one of claims 16 to 20, whereinthe liquid crystal panel has (a) a driving substrate having a substrate,a pixel electrode formed on said substrate and a switching elementconnected to said pixel electrode, (b) an opposite substrate that ispositioned opposite to said driving substrate through a predeterminedspace and has a light-transmitting substrate and an opposite electrodein a position being on said light-transmitting substrate and facing saidpixel electrode, and (c) a liquid crystal layer which is held in apredetermined space formed between said driving substrate and anopposite substrate and is drivable by a voltage upon application of thevoltage between said pixel electrode and the opposite electrode, thedustproof substrate being for use on an outer surface of at least one ofsaid driving substrate and said opposite substrate.